The treatment of gaseous emissions containing volatile organic compounds has been an increasing concern in recent years. Chemical plant off-gas emissions containing volatile organic compounds, particularly halogenated volatile organic compounds, are highly toxic pollutants for the environment and may be dangerous to human beings. Several technologies have been developed for the removal of such chemical plant off-gas emissions including thermal incineration, adsorption, and catalytic oxidation.
Thermal incineration requires high operating temperatures and high capital cost facilities. If the gaseous stream also includes halogenated compounds, thermal incineration can create toxic halogenated compounds under some conventional operating conditions. Thus, thermal incineration may not be effective.
In some circumstances, adsorption by adsorbents, such as carbon, is an alternative process for the removal of such volatile organic compounds from off-gas emissions. However, this process does not destroy the pollutants but merely concentrates them. Furthermore, adsorption efficiency can be adversely impacted by fluctuating concentrations of the volatile organic compounds that may be present in the off-gas emissions.
Alternatively, catalytic oxidation is an energy efficient and economical way of destroying off-gas emissions, such as carbon monoxide and volatile organic compound emissions. Oxidation catalysts, such as precious metal catalysts and base metal catalysts, have previously been used for the destruction of volatile organic compounds and carbon monoxide in chemical plants. However, when the volatile organic compounds to be removed contain halogenated organic compounds, traditional oxidation catalysts cannot be used because they are quickly poisoned by these halogenated organic compounds.
As an example of a current problem in the removal of halogenated organic compounds, off-gas emissions from purified terephthalic acid (PTA) production plants normally contain carbon monoxide, methyl bromide, and various VOCs. Before these off-gases can be vented to the atmosphere, these compounds must be destroyed, normally by catalytic oxidation. Current catalysts used for such oxidation process are required to operate at high temperatures to minimize or eliminate the formation of polybromobenzenes, which are solid and can cause plugging or blockage of process pipe lines.
Although prior art systems have been useful for the treatment of some types of emissions, there is still a need to develop improved catalysts for the destruction of CO and volatile organic hydrocarbons, particularly halogenated VOCs.
The present disclosure provides solutions to the aforesaid problems by offering more active catalytic compositions which oxidize VOCs, particularly halogenated organic compounds, at temperatures lower than are used for conventional oxidation catalysts, and processes for their production and use.